In recent years, development of a technique for tactile presentation has been in progress, which spuriously presents tactile sense felt by a person when touching an object with a finger or the like. In the case of applying the technique of tactile presentation to electronic equipment concerning a liquid crystal display or an organic light emitting diode (OLED) display for example, a tactile presentation device of a panel type for presenting tactile sense is provided on the display. According to an image displayed on the display, the tactile presentation device reproduces tactile sense of an object in the image and causes a user who touches the panel to perceive a sense of touch.
A method of presenting tactile sense employs, for example, an actuator type, an electric stimulus type, an electric vibration type or the like. Among them, the electric vibration type utilizes electrostatic force to present tactile sense on the user's skin.
The tactile presentation device of the electric vibration type comprises an electrode for tactile presentation covered with an insulating film, and applies a voltage signal for tactile presentation to the electrode. Here, the voltage signal for tactile presentation is a voltage signal with frequency at which the mechanoreceptor of human skin has sensitivity. When the user touches the insulating film, electrostatic force is generated between the finger skin and the electrode. If the user slides his/her finger on the surface of the insulating film, variation in the frictional force occurs at the frequency of the voltage signal for tactile presentation, allowing the user to perceive a so-called feel of texture.
The tactile presentation device of the electric vibration type may include multiple electrodes disposed on a substrate, each of which is independently driven so as to partially present tactile sense. For example, Japanese Patent Application Laid-Open Publication No. 2011-248884 discloses a tactile presentation device that partially presents tactile sense by independently driving multiple electrodes for tactile presentation with a driver.
In the tactile presentation device of the electric vibration type, however, some wiring configurations for applying voltage to the electrodes may cause the user to perceive tactile sense which is not necessary. FIG. 1 is a partial enlarged view illustrating a configuration example of a tactile presentation device 110 according to the related art. FIG. 1 illustrates a partial enlarged view in which a part of a panel for tactile presentation is enlarged. As illustrated in FIG. 1, the tactile presentation device 110 according to the related art comprises wirings 111, electrodes 112 and a substrate 113. Multiple electrodes 112 are arrayed in matrix on the substrate 113, while wirings 111 are connected to the respective electrodes 112. The electrodes 112 and wirings 111 are covered with an insulating film which forms a touch surface to be touched by the user.
The electrodes 112 are connected to an external signal voltage source (not illustrated) through the wirings 111. In the case where a voltage signal for tactile presentation is applied from a signal voltage source to one of the electrodes 112 through the corresponding wiring 111, the electrode 112 is electrically charged to present tactile sense to a finger of the user. The tactile presentation device 110 may independently drive each of the electrodes 112, so as to partially present tactile sense.
An example case is discussed where a voltage signal is applied to an electrode 112a through a wiring 111a indicated by a thick line in FIG. 1 to present tactile sense at the electrode 112a. If a finger of the user touches the surface of the insulating film over the electrode 112a, electrostatic coupling occurs between the electrode 112a and the finger skin through the insulating film. The electrostatic force generated between the electrode 112a and the finger skin varies according to the frequency of the voltage signal, causing vibration to the finger. If, on the other hand, the finger touches a part of the surface of the insulating film other than the electrode 112a, no vibration is supposed to occur because no voltage is applied to the other electrodes 112.
However, since voltage is applied to the electrode 112a through the wiring 111a, unnecessary tactile sense may be developed also on the wiring 111a. FIG. 2 illustrates the development of unnecessary tactile sense according to the related art. As illustrated in FIG. 2, in the case where the finger touches the surface of the insulating film in the vicinity of the wiring 111a, a leakage electric field from the wiring 111a may generate electrostatic coupling between the wiring 111a and the finger skin. That is, tactile sense may be perceived at a portion where the tactile sense is not supposed to be perceived. In the description below, the tactile sense which is not necessary as described above is referred to as “unwanted tactile sense.”